Si5345-44-42-D-RM
Rev. 1.0
21
5. Clock Inputs
The Si5342/44/45 support 4 inputs that can be used to synchronize to the internal DSPLL.
5.1. Inputs (IN0, IN1, IN2, IN3)
The inputs accept both standard format inputs and low-duty-cycle pulsed CMOS clocks. Input selection from
CLK_SWITCH_MODE can be manual (pin or register controlled) or automatic with user definable priorities.
Register 0x052A is used to select pin or register control, and to configure the input as shown below in Table 8.
5.1.1. Manual Input Switching
In manual mode, CLK_SWITCH_MODE=0x00.
Input switching can be done manually using the IN_SEL[1:0] device pins from the package or through register
0x052A IN_SEL[2:1]. Bit 0 of register 0x052A determines if the input selection is pin selectable or register
selectable. The default is pin selectable. The following table describes the input selection on the pins. Note that
when Zero Delay Mode is enabled, the FB_IN pins will become the feedback input and IN3 therefore is not
available as a clock input. Also, in Zero Delay Mode, ZDM_EN must be set and register based input clock selection
must be done with ZDM_IN_SEL. If there is no clock signal on the selected input, the device will automatically
enter free-run or holdover mode.
Table 8. Input Selection Configuration
Register Name
Hex Address
[Bit Field]
Function
CLK_SWITCH_MODE
0x0536[1:0] Selects manual or automatic switching modes. Automatic mode can be
revertive or non-revertive. Selections are the following:
00 Manual,01 Automatic non-revertive
02 Automatic revertive, 03 Reserved
IN_SEL_REGCTRL
0x052A [0]
0 for pin controlled clock selection
1 for register controlled clock selection
IN_SEL
0x052A [2:1] 0 for IN0, 1 for IN1,
2 for IN2, 3 for IN3 (or FB_IN)
Table 9. Manual Input Selection using IN_SEL[1:0] Pins
IN_SEL[1:0] DEVICE PINS
Zero Delay Mode Disabled
Zero Delay Mode Enabled
00
IN0
IN0
01
IN1
IN1
10
IN2
IN2
11
IN3
Reserved